The manufacture of automotive vehicles often requires that metallic members be attached to each other. Pierce riveting is one potential method of attaching such members, particularly, steel or aluminum sheets. Pierce riveting typically requires a sharpened end portion of a rivet to pierce through a first of two stacked metallic sheets, and through at least a portion of the second of the stacked sheets. During such piercing, the sharpened end portion of the rivet is typically deformed or bent to secure the rivet to the metallic sheets, thereby interlocking the metallic sheets into an assembly.
For improved weight savings, non-structural metallic members may be replaced with a composite material such as a thermoplastic. Thermoplastics are a polymeric material that becomes pliable and moldable above a specific temperature, which would be ideal in the manufacturing of automotive components such as door panels, body fenders, bumper covers, and the likes. Thermoplastics may be reshaped by heating and formed into automotive components by various polymer processing techniques such as injection molding, compression molding, and extrusion. However, below its glass transition temperature (Tg), thermoplastic composites commonly used in automotive applications, such as fiber reinforced thermoplastics (e.g. polystyrenes, polycarbonates, and poly-vinyl-chlorides), are less ductile and more brittle than that of metallic members.
Self-piercing rivets may be used to join a thermoplastic composite member to a metallic member, or a thermoplastic composite member to another thermoplastic composite member. However, when a rivet is pierced close to an edge of the thermoplastic member, the amount of impact force required to drive the rivet through the members and to deform the sharpened end of the rivet to interlock the two members may result in micro-cracks between the rivet and edge of the less ductile and brittle thermoplastic member, resulting in the weakening of the rivet joint. To compensate, the edge of the thermoplastic member may be extended to increase the overlap of the composite member and the other member. This increased overlap provides sufficient distance between the rivet and the edge of the thermoplastic member to provide the structural integrity necessary to avoid the formation of cracks. However, the increase in length of the thermoplastic member results in increased material usage, weight, and increased in the overall size of the final assembly resulting in a need for a redesign of the form factor of the component.
Thus, there is a need for improved pierce riveting techniques for achieving high integrity attachment of a thermoplastic member to a thermoplastic or non-thermoplastic member while minimizing the overlap of the thermoplastic member with the other member.